[lldb] Fix misleading indentation in ABISysV_x86_64.cpp

[kastiglione]

Pre-emptive fix for eventual use of -Wmisleading-indentation.

See also #2928.

[kastiglione]

@JDevlieghere where do you think the best place is for the cmake addition?

[jasonmolenda]

This is a good change, but should we be pushing for this on llvm github (upstream) instead?

[adrian-prantl]

This is clearly great, I just wonder if escalating this to -Werror is necessary or if we could get by with just enabling the warning. If we just enable the warning, it may be easier to add to the upstream repository, too. The upstream repository needs to be buildable by a much wider range of compilers and compiler versions, so just enabling the warning might be a more palatable change.

[kastiglione]

Upstream: My plan was to merge here first, and then try for upstream. But in that plan I was making an assumption: that we are willing to differ from upstream. But is that true? If people don't want this upstream, do we still want it here?

Warning vs error: I couldn't think of a case where we would want to allow broken indentation. If it's only a warning, we may not see it, and even if we do see it, would it be fixed? A typical build-script invocation has a lot of output, including warnings, so using a warning might be no different than having no warning.

[kastiglione]

Re warning vs error: We may want to use LLVM_ENABLE_WERROR, but my personal opinion is there are plenty of warnings that are innocuous and shouldn't break the build.

[kastiglione]

Let's start with warning, and if we find that's not strict enough we can make it an error as a second step.

[kastiglione]

https://reviews.llvm.org/D102092

[kastiglione]

This is now limited to a fix for -Wmisleading-indentation

[kastiglione]

@swift-ci test